1. Field of the Invention
The present invention relates to a speaker, and more specifically, the present invention relates to a speaker including a substantially hemispherical surface vibrator.
2. Description of the Related Art
A speaker including a hemispherical surface vibrator has been disclosed in Japanese Patent Application No. 7-347884 (Japanese Unexamined Patent Publication No, 9-168194. In this speaker 1, as shown in FIG. 9, electrodes 3a and 3b are provided on both surfaces of a hemispherical surface vibrating body 2 made of a piezoelectric material. By inputting a signal between these electrodes 3a and 3b, the vibrating body 2 vibrates so that an acoustic wave is produced. The edge portion of the vibrating body 2 is attached to a base 4.
In the base 4, a horn portion 5 is provided which has a hole (sound path) that gradually increases in size from the inner surface side of the vibrating body 2 toward the outside. With the horn portion 5, an acoustic wave radiating from the inner surface side of the vibrating body 2, caused by the vibration of the vibrator 2, passes through the horn portion 5 and is directed to the outside. An acoustic wave radiating from the outer surface side of the vibrating body 2 and an acoustic wave radiating from the inner surface side have a phase difference of 180xc2x0. However, the sound waves are manipulated by the horn portion 5 such that the sound waves are in substantially the same phase in a direction parallel to the installation plane of the speaker 1.
As described above, in this speaker 1, since the vibrating body 2 has a hemispherical surface shape, an acoustic wave is radiated omnidirectionally from the curved outer surface side of the vibrating body 2. Further, an acoustic wave radiated from the inner surface side of the vibrating body 2, passing through the sound path of the horn portion 5, is radiated omnidirectionally in the direction parallel to the installation plane of the speaker 1. Accordingly, this speaker 1 can be used as a non-directional speaker. Further, a speaker that converts electric signals to acoustic signals very efficiently is produced, due to the utilization of an acoustic wave radiated from the outer surface side of the vibrating body 2 and also an acoustic wave radiated from the inner surface side thereof.
However, since such a speaker utilizes an acoustic wave radiated from the inner surface side of the vibrating body, the speaker must include an integrally formed base and horn portion. Regarding the shape of the hole provided in the horn portion, the hole is shaped such that it gradually increases in size from the inner surface side of the vibrating body to the outside. This shape is difficult to manufacture, and thus the base and the horn portion are difficult to produce. To effectively utilize a sound wave radiated from the inner surface side of the vibrating body, a gap between the base and the vibrating body-must be accurately maintained. Thus, the production of such a speaker requires close tolerances which increases the cost and difficulty of manufacturing.
Accordingly, preferred embodiments of the present invention provide a speaker including a substantially hemispherical surface vibrating body that is economically manufactured.
According to a preferred embodiment of the present invention, a speaker includes a substantially hemispherical surface vibrator, a driving mechanism arranged to vibrate the vibrator, and a flat base plate to fix the edge portion of the vibrator.
In such a speaker, the vibrating body is made of a piezoelectric material, and the driving mechanism includes electrodes provided on the inner surface and the outer surface of the vibrator.
Further, the speaker includes a horn disposed on the outer surface side of the vibrator and having a hole that gradually increases in diameter as the distance from the vibrator increases.
Moreover, the horn reflects an acoustic wave produced by vibration of the vibrator, and further vibrates with the vibration of the vibrator.
In a preferred embodiment of the present invention, the horn is fixed to a flat base plate.
In the speaker according to another preferred embodiment of the present invention, only an acoustic wave radiated from the outer surface side of the hemispherical surface vibrating body is utilized. Thus, it is unnecessary to provide a horn portion that is integral with a base because the speaker does not utilize an acoustic wave radiated from the inner surface side. Therefore, the base arranged to fix the edge portion of the hemispherical surface vibrating body is configured to have a flat plate shape, and the speaker is therefore economically produced.
The substantially hemispherical surface vibrating body is made of a piezoelectric material, or other suitable material. To drive the vibrating body, electrodes are provided on the both surfaces of the vibrating body.
Further, by attaching a horn having a gradually increasing diameter toward the outside to the outer surface side of the vibrating body, an acoustic wave that is radiated from the outer surface side of the vibrating body and reaches the inner surface of the horn is reflected. Thus, the directions of sound waves to be radiated from the speaker are accurately set, and the sound pressure level in the radiation direction is greatly improved.
By configuring the speaker so that the horn is vibrated with the vibration of the vibrating body, the sound pressure level in the bass is greatly improved.
Other features, elements, characteristics and advantages of the present invention will become apparent from the detailed description of preferred embodiments thereof with reference to the drawings attached hereto.